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Biomedical subjects

A M Fischer

Publications and source records attributed to A M Fischer.

At least 37 records · Page 2Linked to original sources
PubMed1998

Diagnostic value of two rapid and individual D-dimer assays in patients with clinically suspected pulmonary embolism: comparison with microplate enzyme-linked immunosorbent assay.

A semiquantitative enzyme-linked immunosorbent assay (ELISA) test (Instant IA D-dimer) and a new quantitative rapid and individual test (STA-Liatest DDi) were compared with the reference microplate ELISA (Asserachrom D-Di) for D-dimer testing in 142 patients clinically suspected of pulmonary embolism, on the basis of clinical symptoms and signs, electrocardiogram, blood gases and chest X-Ray abnormalities. The cut-off value for the quantitative tests was 500 ng/ml and Instant IA was interpreted by three readers. Pulmonary embolism was confirmed by lung scan or angiography in 60 patients (42%). The sensitivities of ELISA and STA-Liatest DDi were 92% [95% confidence interval (CI) 82-97%] and 93% (95% CI 84-98%), respectively. The three readings of Instant IA D-dimer disagreed in 27 (19%) of the patients and sensitivity varied from 83 to 93% according to the readers. In the 115 patients with concordant readings, sensitivity was 92% (95% CI 82-98%). These results suggest that STA Liatest DDi may be used instead of microplate ELISA for the exclusion of pulmonary embolism, whereas the use of Instant IA D-dimer for this purpose is limited by the number of discordant results.

Adult↗
PubMed1998

Fucoidan, as heparin, induces tissue factor pathway inhibitor release from cultured human endothelial cells.

Fucoidan, a sulfated polysaccharide extracted from brown seaweeds, has antithrombotic properties, the mechanism of which is not yet completely understood. Tissue factor pathway inhibitor (TFPI), which regulates the tissue factor-dependent pathway of blood coagulation, is released from the endothelium by heparin, a mechanism contributing to its antithrombotic activity. In this study, we demonstrated that fucoidan, as heparin, induces TFPI release from cultured human umbilical vein endothelial cells (HUVEC). The TFPI accumulation in the HUVEC supernatants depends on the incubation time and polysaccharide concentration. After 30 to 60 minutes of incubation, TFPI concentration (total antigen level) was twice higher in the presence of both polysaccharides than in their absence. After one hour of incubation, in the presence of increasing concentrations of each polysaccharide, an optimal stimulation was observed for 0.5 microg/ml of fucoidan and 5 microg/ml of heparin, as evidenced by a raise of the basal TFPI level: a 2-fold increase for the total antigen and a 3-fold increase for the free antigen. These data suggest that TFPI released from vascular endothelial cells may contribute to the antithrombotic effect of fucoidan.

Anticoagulants↗
PubMed1997

Mechanism of thrombin inhibition by heparin cofactor II in the presence of dermatan sulphates, native or oversulphated, and a heparin-like dextran derivative.

The kinetics of thrombin inhibition by heparin cofactor II (HC II) in the presence of dermatan sulphates, native (DS), or oversulphated (DSS 1 and DSS 2) and a biospecific dextran derivative substituted with carboxymethyl, carboxymethyl-benzylamide and carboxymethyl benzylamide-sulphonate functional groups (CMDBS), has been studied as a function of the sulphated polysaccharide concentration. The initial HC II and thrombin concentrations were set at equimolar levels. Analysis of the experimental data obtained for DS, DSS1 and DSS2 was performed using a previously described model which allows computation of the dissociation constant (KPS,HC) of the polysaccharide-HC II complex and the rate constant of thrombin inhibition by the polysaccharide-HC II complex (k). A KPS.HC of 9.6 x'10(-7) M and a k of 4.5 x 10(9) M-1 min-1 were found for DS, whereas KPS,HC 2.1 x 10(-6) M, k 1.1 x 10(10) M-1 min-1 and KPS,HC 4.3 x 10(-7) M, k 1.4 x 10(10) M-1 min-1 were found for DSS1 and DSS2, respectively. Knowing that DSS1 has a sulphur content per disaccharide of 7.8%, compared with 11.5% for DSS2, these results indicate that the polysaccharide affinity for HC II is increased only in the case of DSS 2, whereas the oversulphation increases the reactivities towards thrombin of both complexes DSS1-HC II and DSS2-HC II. A better conformation of these complexes may favour a faster interaction with the protease. Unlike heparin, DS at concentrations higher than 10(-5) M does not modify the reaction rate of thrombin inhibition, a fact which can be explained by the absence of complex formation between DS and thrombin. The experimental data obtained for CMDBS fit a kinetic model in which the biospecific dextran derivative rapidly forms a complex with thrombin which is more reactive towards HC II than the free protease. The reaction rate remained unchanged for CMDBS concentrations equal to or higher than 10(-5) M, whereas CMDBS was found to interfere strongly with the fibrinogen-thrombin interaction. These data suggest that CMDBS has a strong affinity for the protease and no affinity for HC II. The computed dissociation constant of the CMDBS-thrombin complex (KPS,E) was 2.4 x 10(-7) M and the rate constant of the reaction of this complex with HC II (k) was 1.7 x 10(8) M-1 min-1. These findings indicate that CMDBS exerts its catalytic effect through a unique mechanism of action and may constitute a new class of anticoagulant drugs.

Dermatan Sulfate↗
PubMed1997

Mechanism of thrombin inhibition by antithrombin and heparin cofactor II in the presence of heparin.

The kinetics of thrombin inhibition by antithrombin (AT) and heparin cofactor II (HC II) were analysed as a function of the heparin concentration, from 10(-9) to 10(-4) M. The initial concentrations of inhibitor (l) and thrombin (E) were set at equimolar levels (CI = CE = 10(-8) M). The experimental data indicate that the reaction of thrombin inhibition was second-order both in the absence and in the presence of heparin, and that the apparent rate constant increased at heparin concentrations ranging from 10(-9) to 10(-6) M and decreased at higher concentrations. The data fit with the kinetic model established by Jordan et al. [J. Biol. Chem. 1979, 254, 2902-2913] for the catalysis of the thrombin-AT reaction by a low-molecular-weight heparin fraction. In this model, heparin (H) binds quickly to the inhibitor (I) and forms a heparin-inhibitor complex (HI), which is more reactive than the free inhibitor towards thrombin, leading to the formation of an inactive inhibitor-thrombin complex (I*E) and the release of free heparin, in a second step which is rate limiting. KH,I, the dissociation constant of HI, and k, the second-order rate constant of free thrombin inhibition by HI, were found to be 3.7 x 10(-7) M and 1.3 x 10(9) M-1 min-1, respectively, for AT, compared to a KH,I of 2.0 x 10(-6) M and k of 6.4 x 10(9) M-1 min-1 for HC II. These data indicate that heparin-HC II complex reactivity is greater than that of the heparin-AT complex towards thrombin, whereas heparin affinity is stronger for AT. At heparin concentrations higher than 10(-6) M, the decrease in the reaction rate was in keeping with the formation of a heparin-thrombin complex (HE), whose inactivation by the heparin-inhibitor complex (HI) is slower than that of the free protease.

Antithrombins↗
PubMed1997

Interactions of poly(lactic acid) and poly(lactic acid-co-ethylene oxide) nanoparticles with the plasma factors of the coagulation system.

When surfactant-stabilized biodegradable poly(lactic acid) (PLA) particles are injected into rats, the rate of clearance from blood is fast. The rate can be strongly reduced by using particles made from diblock copolymers of PLA and poly(ethylene oxide) (PLA-PEO), resulting in an increased duration of contact with the components of the coagulation system. Thus, possible adverse effects such as activation of the coagulation cascade could occur. In this paper, the interactions of surfactant-stabilized PLA and PLA-PEO nanoparticle suspensions with the plasma factors of the coagulation system are presented. PLA suspensions stabilized by sodium cholate (PLA-Ch) interact with thrombin, factor V and calcium ions. Formation of complexes and aggregates is induced by addition of calcium ions to PLA-Ch suspensions in the presence or in the absence of plasma. On the contrary, PLA-PEO suspensions are remarkably inert towards the coagulation factors and calcium ions, even when cholate is present. Steric repulsion owing to the high surface density of PEO is sufficient to avoid strong interations with the proteins and formation of aggregates between particles.

Blood Coagulation↗
PubMed1996

Heparin-like functionalized polymer surfaces: discrimination between catalytic and adsorption processes during the course of thrombin inhibition.

Thrombus formation on blood-contacting artificial surfaces is a major problem. Antithrombogenic polymer surfaces have been obtained either by heparin binding, or by grafting sulphonate and/or amino acid sulphonamide groups on insoluble polystyrene. In addition to their capacity to adsorb thrombin, such surfaces were shown to be able to catalyse its inhibition by antithrombin III (AT), i.e. they are endowed with heparin-like activity. The results were mainly obtained by using clotting assays. In many cases, delineating adsorption and catalytic processes by such assays is not possible when evaluating anticoagulant polymer surfaces. To overcome this problem, the kinetics of thrombin adsorption and inhibitions by AT and heparin cofactor II (HC) in the presence of such surfaces have been measured by using an assay performed with a thrombin-specific chromogenic substrate. A simple kinetic model of thrombin consumption is proposed. The relevant calculations, carried out with the help of a computer program, lead to determination of relative second order rate constants of thrombin adsorption and inhibitions by AT and HC in the presence of the polymers. In addition to thrombin adsorption, polystyrene surfaces bearing only sulphonate groups catalyse inhibition by AT, whereas polystyrene surfaces bearing either aspartate, glycinate or isophthalate sulphonamide groups catalyse both inhibitions by AT and HC.

Adsorption↗
PubMed1996

Heparin-induced thrombocytopenia with thrombotic complications during prophylactic treatment with low-molecular-weight heparin.

Heparin-induced thrombocytopenia is very uncommon with low-molecular-weight heparin, especially when given for prophylaxis of venous thromboembolism. In two of the four published cases, with thrombotic complications, thrombocytopenia may have been related to cross-reactivity between unfractionated heparin and low-molecular-weight heparin. We report one patient who received low-molecular-weight heparin for prophylaxis against venous thromboembolism without any previous injection of unfractionated heparin, and experienced thrombocytopenia with thrombotic complications. Heparin-induced thrombocytopenia was confirmed by several laboratory assays. This observation emphasizes the need for platelet count monitoring during low-molecular-weight heparin therapy.

Aged↗
PubMed1995

Recombinant hirudin (HBW 023): biological data of ten patients with severe venous thrombo-embolism.

This study reports on the biological data of ten patients with acute venous thrombo-embolism. They were treated for 5 days with continuous intravenous infusion of a fixed dose (0.05 mg/kg/hr) of a recombinant hirudin (r-H HBW 023 Behringwerke, Germany). The plasma level of r-H (HBW 023), assessed by an anti-factor IIa amidolytic activity, was stable after Day 2 and showed considerable individual variations. It correlated with APTT ratio, suggesting that this test is a reliable tool to monitor therapy. In contrast, thrombin time was constantly over 120 sec (control 15 sec) and consequently was not a useful parameter. Prothrombin time showed a slight, but significant, prolongation, which was correlated with the increase of APTT ratio. There was no bleeding time prolongation, platelet count, or ATIII level decrease. Levels of thrombin-antithrombin III complexes, and D-dimers, which were high in all patients on admission, decreased during the course of the treatment but remained abnormal on Day 5, showing an ongoing hemostasis and fibrinolysis activation: this is consistent with the delayed, but only slightly decreased thrombin generation evidenced by thrombin generation test performed on Day 3. These results suggest that thrombin inhibition by rH-hirudin at this dosage is only partial, which allows the generation of traces of thrombin needed for the feed-back thrombin production generated by factor V and VIII activation.

Adult↗
PubMed1995

Severe hypofibrinogenemia associated with bilateral ischemic necrosis of toes and fingers.

Severe hypofibrinogenemia was found in an Algerian woman who, since the age of 37 years, suffered three different episodes of ischemic necrosis of the toes and fingers leading to amputation of the toes and surgical removal of necrotic tissue (necretomy). No anti-fibrinogen antibody was present. The deficiency appeared to be due to severe congenital hypofibrinogenemia since the fibrinogen level remained at the same low level over a long period, without any abnormality of other coagulation proteins. The thrombotic events may be explained by the increased thrombin generation observed in the patient's plasma, due to the lack of thrombin adsorption onto a fibrin net.

Adult↗
PubMed1995

Venous antithrombotic and anticoagulant activities of a fucoïdan fraction.

Fucoïdans catalyse thrombin inhibition by antithrombin (AT) and heparin cofactor II (HCII); their affinity for each serpin varies according to the seaweed species from which they are extracted, as well as their chemical composition and molecular weight. We extracted a homogeneous fucoïdan fraction from Ascophyllum nodosum, a brown seaweed, and tested its anticoagulant and antithrombotic activities. At a fucoïdan concentration of 3.75 micrograms/ml, thrombin inhibition mediated by AT showed an apparent second-order rate constant (kapp) of 2 x 10(8) M-1 min-1, compared to 1.5 x 10(6) M-1 min-1 for the uncatalyzed reaction. The kapp value of thrombin inhibition via HCII was 1.17 x 10(9) M-1 min-1 at a fucoïdan concentration of 50 micrograms/ml, compared to 1.72 x 10(5) M-1 min-1 for the uncatalyzed reaction. In a Wessler model of venous thrombosis, the fucoïdan fraction, injected intravenously to rabbits 10 min before thrombosis induction, exhibited antithrombotic activity: 1.8 mg/kg was the dose which inhibited F Xa-induced thrombus formation by 80% (ED80), compared to a heparin ED80 of 0.1 mg/kg. At this ED80 the antithrombotic effect of the fucoïdan persisted longer than that of heparin (30 min versus 15 min). The thrombin clotting time (TCT) was significantly prolonged (73 s versus control 29 s, compared to 53 s with heparin) 10 min after a fucoïdan bolus infusion giving a plasma fucoïdan concentration of 14.6 +/- 2.7 micrograms/ml. The bleeding time was slightly increased after fucoïdan infusion at the ED80. Fucoïdan extracted from marine flora thus shows promise as an antithrombotic drug.

Animals↗
PubMed1994

Acquired factor VII deficiency associated with pleural liposarcoma.

Isolated acquired factor VII (FVII) deficiency (0.15 U/ml) was identified in a 30-year-old man with pleural liposarcoma. The patient underwent surgery with continuous FVII concentrate infusion. No anti-FVII antibody or FVII/anti-FVII complex was detected. However, the short half-life and low recovery of FVII after concentrate infusion suggested the presence of an antibody. Whatever the mechanism, this FVII deficiency was related to the presence of the liposarcoma. FVII level normalized during tumour regression and fell again when the liposarcoma relapsed.

Adult↗
PubMed1993

Affinity chromatography of sulphated polysaccharides separately fractionated on antithrombin III and heparin cofactor II immobilized on concanavalin A--sepharose.

Three sulphated polysaccharides, dermatan sulphate, fucan and heparin, were fractionated according to their affinity towards antithrombin III (ATIII) and heparin cofactor II (HCII), the two main physiological thrombin (IIa) inhibitors. Both inhibitors were immobilized on concanavalin A-Sepharose, which binds to the glycosylated chains of the proteins while the protein-binding site for the polysaccharide remains free. Each polysaccharide was fractionated into bound and unbound fractions either for ATIII or HCII. The eluted fractions were tested for their ability to catalyse ATIII/IIa and HCII/IIa interactions. The possible presence of a unique binding site for ATIII and HCII, on each sulphated polysaccharide, was also studied.

Animals↗
PubMed1993

Human umbilical vein endothelial cell culture on heparin-like microcarriers.

Biospecific functional polymers, i.e., polymers randomly substituted with specific chemical functional groups, were designed to interact with living systems. Interactions between polystyrene sodium sulfonate (PSSO3Na) and insulin secreting RINm5F cells have been previously described. For the sake of comparison, interactions of PSSO3Na with human umbilical vein endothelial cells (HUVEC) were studied. In this case, the interaction is indirect, i.e., mediated by a binding protein, fibronectin (Fn). This was evidenced by HUVEC culture on Fn precoated PSSO3Na microcarriers. The interactions between PSSO3Na and HUVEC result in a biologically normal proliferation of cells and synthesis and secretion of Von Willebrand Factor (VWF). These results show that different biospecific interactions may occur between cells in culture, binding proteins and polymers randomly substituted with suitable functional groups. HUVEC, when cultured on heparin-like microcarriers, behave differently from other cells like RINm5F, whose interaction with the same polymers is not mediated by binding proteins.

Adsorption↗